Shire is to acquire San Diego-based Meritage Pharma for $70m (£45m) in a move that will add another drug for a rare gastrointestinal disorder to its pipeline.

The FTSE 100 company will also make additional, undisclosed, payments to Meritage if it passes certain drug development milestones.

The deal comes hot on the heels of Shire's $5.2bn acquisition of NPS Pharma in January, and analysts do not expect it to be the last. Flemming Ornskov, chief executive, has made clear that Shire will buy up companies with drugs that fit with its aims of expanding its rare disease portfolio, helped by a $1.6bn windfall from its collapsed tie-up with AbbVie.

Meritage Pharma is developing a treatment for a rare allergic reaction known as eosinophilic oesophagitis (EoE), which causes the oesophagus, or food pipe, to swell up, making it difficult to swallow.

Doctors currently treat the condition by recommending changes in diet to avoid foods which trigger the reaction.

They also administer steroids mixed with sugar syrup to coat the oesophagus and reduce inflammation - though no treatment specifically designed for EoE is on the market. Meritage is hoping to fill this niche with its suspension of the steroid budesonide, which is now ready to enter its third and final stage of human trials.

Shire inherited the right to acquire Meritage with its $4.2bn takeover of rare disease specialist Viropharma in 2013. Viropharma had two years earlier bought an exclusive option to acquire Meritage Pharma for $69.9m at its point of entry into phase three clinical trials.

Philip J Vickers, head of research and development at Shire, said the acquisition would "complement our strong GI capabilities". Shire's late-stage pipeline also includes a treatment for non-alcoholic steatohepatitis, a condition resulting from the build-up of fat in the liver which can lead to permanent damage.

Elaine Phillips, president and chief executive of Meritage, said the deal with Shire meant the drug could progress through the next stages of development.

"The acquisition...may benefit physicians and patients by helping develop OBS to potentially become the first approved treatment in the U.S. indicated for this often disabling disease,” she said.

Shire said it did not expect the acquisition to affect its earnings outlook for 2015.